tools/libxc: Improve the *_FIELD() macros

tools/libxc: Improve the *_FIELD() macros

The {GET,SET,MEMCPY,MEMSET_ARRAY}_FIELD() macros previously required
'dinfo->guest_width' to exist in scope, which is somewhat antisocial, and
makes them awkward to use in other contexts.

Update these macros to take guest width as a parameter, and in all cases pass
dinfo->guest_width.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>